The rapid development of the telecommunications industry have made wireless handheld devices like cell phones, pagers, two-way messaging devices, etc. massively popular, creating a need for new electronic components and circuits in both mobile and base station systems as competition drives the introduction of expanded capabilities.
For wireless handsets, wireless PDAs (Personal Digital Assistants), and other wireless devices, one overarching concern is power consumption; the less power a device consumes the more desirable it is. Thus higher efficiency components, such as amplifiers, are desirable in these wireless devices.
Radio frequency power amplifiers contribute to the power consumption in the communications systems. To extend battery life in mobile units, and to reduce operating costs of base stations, there is a need to develop new amplifiers to replace inefficient, power wasting, elderly designs currently in use.
Many contemporary base station amplifiers employ complex techniques to realize amplifiers with a high degree of linearity over a broad frequency range. Unfortunately those solutions have a low efficiency.
Handset power amplifiers also suffer from efficiency problems, often more critical than those for base stations as the power supply for mobile user equipment is strictly limited. Today's smaller, faster and more effective portable electronics demand high power with only little losses.
Switching mode amplifiers have been used for quite some time in various electronic systems including audio power amplifiers and switching power supply circuits. In switching mode amplifiers, the transistor is operated as a switch. Switching mode amplifiers suffer however from the existence of some fundamental limits, such as large parasitic capacitance, which may prevent many transistors from working well at high power and frequency.
Modulation schemes incorporating an amplitude component is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. Amplitude modulation works by varying the strength of the transmitted signal in relation to the information being sent. For example, changes in the signal strength can be used to reflect the sounds to be reproduced by a speaker. Unfortunately, amplifiers loose efficiency when working in backed of power operation i.e. working below full effect, why they at present are unsuitable to be used for amplitude modulation of a radio signal. Thus there is a problem with efficiency in back off.
One type of architecture to circumvent this is the so called Linear amplification using Nonlinear Components (LINC) or the Chireix architecture. These techniques are commonly known as outphasing which involves two signals which are separated by a common phase angle and recombined in a combiner or combining network. By adjusting the said phase of the two signals, the combined resulting signal presents an amplitude component with amplitude proportional to the said phase difference. This technique enables the use of saturated amplifiers or switching amplifiers to create modulation schemes with amplitude components. Unfortunately, field tests have resulted in far from ideal results, as the resulting circuits were found to be insufficiently efficient, especially in backed of power operation. Also, an uneven workload between the branches shows up when the output power is controlled by altering the outphasing angle. The efficiency is degraded by unwanted power dissipation caused by collisions between the intrinsic drain-voltage and -current.
Based on the above, there is a need for methods or circuits which overcome or mitigate at least some of the drawbacks of the known amplifiers.